The present invention relates to a method and an apparatus of chemical vapor deposition using an organic metal material and, more particularly, to such method and apparatus for growing a high dielectric substance film and/or a ferroelectric film used for a capacitor, an insulated gate transistor and the like.
As micronization and integration density of a semiconductor device have been increased, such ceramic materials have been required as possessing a high dielectric constant and a ferroelectric constant for a capacitor and/or an insulated gate transistor. In applying such ceramic materials to the semiconductor device it is extremely important to deposit the ceramic materials as thin as possible on a semiconductor substrate.
For a deposition method of the thin film, many methods such as a sol-gel method and a sputtering method have been proposed. However, a chemical vapor deposition method is expected to be excellent and promising in uniformity for a large diameter wafer and in a coverage for a step difference.
Metals which are constituent elements of the ceramic material possessing a high dielectric constant and a ferroelectric constant are Ba, Sr, Bi, Pb, Ti, Zr, Ta, La and the like because of hardly obtaining proper hydride and chloride. For this reason, a chemical vapor deposition method employing organic metals, i.e. MOCVD method, is used. However, these organic metals exhibit a low vapor pressure, and many of them are in solid or liquid state under a condition of a room temperature. To transport the organic metals of low vapor pressure, raw materials of them and pipes for their passage are heated. For this reason, a mass flow controller can not be used for these organic metals so that it is difficult to precisely control the flow rate.
For a organic metal vapor phase growth method, a transportation method using carrier gas has been used. FIG. 2 shows a conventional reaction gas supply method where a carrier gas is used. In FIG. 2, reference numeral 201 denotes a constant temperature chamber; 202, a bottle; and 203, an organic metal raw material prepared in the bottle 202, which is, for example, strontium-bis-di-piballoymetanat Sr (DPM).sub.2 and Barium-bis-di-piballoymetanat Ba (DPM).sub.2 and is kept at a solid state at a normal temperature. Reference numeral 204 denotes a supply pipe of inert carrier gas such as Ar and N.sub.2, and reference numeral 205 denotes a supply pipe of the organic metal raw material gas transported by the carrier gas from the pipe 204. This raw material gas is supplied to a growth chamber 207 including a heating mechanism 206 on which a semiconductor wafer 208 is disposed. The exhaustion of gases is performed through a port 209. The reference numeral 210 indicates a mass flow controller for the carrier gas.
In this apparatus, in the case where the organic metal gas kept at a solid state at a normal temperature is used as described above, in order to produce sufficient vapor pressure, the bottle and the supply pipe must be heated to a high temperature unlike the case where a raw material keeping a gaseous state at a normal temperature is used. Since a flow meter capable of being used at a high temperature has not been developed yet, it is difficult to quantify the flow rate of the organic metal gas in the carrier gas and to accurately control the flow rate. Specifically, an organic metal compound such as DPM exhibiting a vapor pressure more than a saturation vapor pressure, which is determined by a temperature at the constant temperature chamber 201, is contained in the carrier gas. The flow rate of the organic metal raw material gas is determined depending on a surface area of a solid of the organic metal compound raw material and a temperature of the constant temperature chamber as well as the flow rate of the carrier gas and the like. However, it becomes difficult to accurately control the flow rate because of many parameters as described above.
For these reasons, the flow rate of the organic metal raw material has been reversely calculated by analyzing the grown thin film, in order to establish appropriate process conditions. Many parameters involve the change with the passage of time so that it has been difficult to form the film with a high reproducibility.